Contact-less tag with signature, and applications thereof

ABSTRACT

A method which comprises generating a first signature by encoding an identifier with a first additional data set at a first time instant; responding to a first read request from a tag reader by releasing the first signature; generating a second signature by encoding the identifier with a second additional data set at a second time instant, the second additional data set being different from the first additional data set; and responding to a second read request by releasing the second signature. Also, a method which comprises obtaining a signature from a contactlessly readable tag; decrypting the signature with a key to obtain a candidate identifier and a scrambling code associated with the signature; and validating the candidate identifier based on at least one of the scrambling code and the signature.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, and claims the benefit under 35 USC120, of International Application No. PCT/CA2007/002343 filed on Dec.20, 2007 and hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to contact-less tags and, morespecifically, to a contact-less tag having a signature as well as toapplications using the properties of such a tag.

BACKGROUND

Contact-less tags, such as radio frequency identification (RFID) tags,are becoming increasingly commonplace in various commercialapplications, two non-limiting examples of which include access controland inventory management.

An RFID tag affixed to an item stores a code (e.g., a bit pattern) thatis output in contactless fashion to a reader, either in response to arequest from the reader or autonomously by the tag. The reader capturesthe bit pattern and then an action may be taken, depending on thecommercial application at hand. For example, in an access controlscenario, the captured bit pattern may reveal that the person presumedto be carrying the tag (by virtue of an association with the bitpattern) is—or is not—authorized to enter a building or operate avehicle. In an inventory management scenario, the bit pattern may givean indication of items contained on a pallet, for example, which mayresult in certain decisions being taken regarding shipping or storage ofthese items.

In both cases, the ease with which an RFID tag may be read by a readerenables rapid processing but also may lead to problems. In the accesscontrol scenario, for example, an RFID tag of an individual authorizedto access certain property may be interrogated and then the bit patterncloned for use by an impostor to gain what is in fact unauthorizedaccess to such property. Similarly, in the inventory managementscenario, an acquired knowledge of the bit pattern associated with acertain item may allow a malicious party to gain intelligence aboutinventory locations that the item's rightful owner (which may includethe manufacturer all the way down to the retail customer) may wish tokeep secret.

In both of the above scenarios, it is apparent that what is relevant toa malicious party is the knowledge that a certain bit pattern output bya certain RFID tag will either give access to property or indicate thepresence of a specific inventory item. Whether the bit pattern is itselfan encrypted version of some original data is actually of no relevanceto the malicious party. Thus, schemes based on straightforwardencryption of the bit pattern do not mitigate the problems mentionedabove.

Against this background, there is clearly a need in the industry for acontact-less tag having improved properties.

SUMMARY OF THE INVENTION

A first broad aspect of the present invention seeks to provide a method,which comprises generating a first signature by encoding an identifierwith a first additional data set at a first time instant; responding toa first read request from a tag reader by releasing the first signature;generating a second signature by encoding the identifier with a secondadditional data set at a second time instant, the second additional dataset being different from the first additional data set; and respondingto a second read request by releasing the second signature.

A second broad aspect of the present invention seeks to provide anapparatus, which comprises means for generating a first signature byencoding an identifier with an additional data set at a first timeinstant; means for responding to a first read request from a tag readerby releasing the first signature; means for generating a secondsignature by encoding the identifier with a second additional data setat a second time instant, the second additional data set being differentfrom the first additional data set; and means for responding to a secondread request from a tag reader by releasing the second signature.

A third broad aspect of the present invention seeks to provide acomputer-readable medium, which comprises computer-readable program codewhich, when interpreted by a computing apparatus, causes the computingapparatus to execute a method. The computer-readable program codecomprises first computer-readable program code for causing the computingapparatus to generate a first signature by encoding an identifier withan additional data set at a first time instant; second computer-readableprogram code for causing the computing apparatus to respond to a firstread request from a tag reader by releasing the first signature; thirdcomputer-readable program code for causing the computing apparatus togenerate a second signature by encoding the identifier with a secondadditional data set at a second time instant, the second additional dataset being different from the first additional data set; and fourthcomputer-readable program code for causing the computing apparatus torespond to a second read request from a tag reader by releasing thesecond signature.

A fourth broad aspect of the present invention seeks to provide a devicefor use in contactless communication with a reader, which comprises amemory configured to store a first signature generated by encoding anidentifier with a first additional data set at a first time instant; anda controller configured to generate a new signature by encoding theidentifier with a second additional data set at a second time instant,the second additional data set being different from the first additionaldata set. The controller is further configured to cause the newsignature to be stored in the memory after the second time instant.

A fifth broad aspect of the present invention seeks to provide a devicefor use in contactless communication with a reader, which comprises amemory configured to store a signature that encodes a pre-determinedidentifier; a transceiver configured to contactlessly receive readrequests from the reader and to contactlessly transmit responsesthereto; a controller configured to respond to read requests receivedvia the transceiver by releasing via the transceiver a current versionof the signature stored in the memory, wherein the version of thesignature stored in the memory varies over at least two time instantswhile continuing to encode the pre-determined identifier; and a powersource for powering at least the controller.

These and other aspects and features of the present invention will nowbecome apparent to those of ordinary skill in the art upon review of thefollowing description of specific embodiments of the invention inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram of a system comprising a reader and a tag, inaccordance with a non-limiting embodiment of the present invention.

FIG. 2 is a block diagram showing details of the tag, in accordance witha non-limiting embodiment of the present invention.

FIG. 3 illustrates a decoding function implemented by a controller inthe tag, for generation of a signature at two points in time.

FIGS. 4A and 4B depict two possible functional architectures forgeneration of a signature.

FIG. 5 illustrates application of an embodiment of the present inventionin an inventory management context.

FIG. 6A shows application of a non-limiting embodiment of the presentinvention in a validation context.

FIG. 6B is a block diagram of a multi-reader architecture, in accordancewith a non-limiting embodiment of the present invention.

FIG. 7A is a flowchart showing operation of a processing entity of FIG.6 when considering tags whose signatures encode a variable scramblingcode and that are encrypted using a common key that is known to thereader or can be determined from an index supplied with the signature.

FIG. 7B is a flowchart similar to that of FIG. 7A, but where the commonkey is unknown to the reader.

FIG. 8 shows application of a non-limiting embodiment of the presentinvention in an identification context when considering tags whosesignatures are encrypted using a variable key.

FIG. 9 is a flowchart showing operation of a processing entity of FIG. 8when considering tags whose signatures are encrypted using a variablekey.

It is to be expressly understood that the description and drawings areonly for the purpose of illustration of certain embodiments of theinvention and are an aid for understanding. They are not intended to bea definition of the limits of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, there is shown a system comprising a reader 12and a tag 14. Communication between the reader 12 and the tag 14 occursover a contact-less medium 16. In a specific non-limiting embodiment,the contact-less medium 16 is a wireless medium that may include aspectrum of radio frequencies. Depending on the application at hand, thetag 14 could be affixed to: an item for sale, goods duringtransportation, a person's clothing, an animal, a piece of equipment(including communications equipment such as wireless communicationsequipment) and so on. For its part, the reader 12 can be fixed ormobile. In the fixed scenario, the reader 12 could be located at anydesired position within a building, vehicle, warehouse, campus, etc. Inthe mobile scenario, the reader 12 could be implemented in a handheld orportable unit, for example.

FIG. 2 shows details of the tag 14, in accordance with a specificnon-limiting embodiment of the present invention. The tag 14 comprises amemory 202, a transceiver 204 (including an antenna), a controller 206and a power source 208.

The memory 202 stores a current signature 212. In addition, the memory202 may store a program for execution by the controller 206, includingcomputer-readable program code for causing the controller 206 to executevarious steps and achieve wide-ranging functionality. In a non-limitingembodiment, the current signature 212 can take the form of a bit patternhaving a certain number of bits. In accordance with an embodiment of thepresent invention, the bit pattern exhibited by the current signature212 is dynamic, that is to say the current signature 212 changes overtime.

The controller 206 executes various functions that allow communicationto take place via the transceiver 204 between the tag 14 and an externalreader such as the reader 12. In what follows, communications willhereinafter be referred to as occurring with the reader 12 although itwill be appreciated that the tag 14 may communicate similarly with otherexternal readers that it encounters.

As part of its functionality, the controller 206 is operative toretrieve the current signature 212 from the memory 202 and to releasethe current signature 212 via the transceiver 204. Alternatively,depending on the computational capabilities of the controller 206, thecontroller 206 can be operative to compute the current signature 212 ondemand and to release via the transceiver 204 the current signature 212so computed.

It is recalled that in this embodiment, the current signature 212 isdynamic. Accordingly, the controller 206 is operative to communicatewith the memory 202 in order to change the bit pattern of the currentsignature 212 stored in the memory 202. This can be achieved byexecuting diverse functionality that will be described in greater detaillater on, and which may include implementing functional elements such asan encryption engine 222, a counter 230, a pseudo-random numbergenerator 240, a geo-location module 250 and a clock module 260, amongothers.

The configuration of the power source 208 and its inter-relationshipwith the controller 206 depend on whether the tag 14 is categorized as“passive”, “active” or somewhere in between. Specifically, the tag 14may be designed as “passive”, whereby transmissions of the currentsignature 212 via the transceiver 204 are effected in response todetection of a burst of energy via the transceiver 204, such burst ofenergy typically coming from the reader 12 issuing a “read request”. Inthis case, the controller 206 only needs to be powered during the shorttime period following the detection of the burst. In fact, the burstitself can charge the power source 208 for a brief period, enough toallow the controller 206 to cause transmission of the current signature212 via the transceiver 204 in response to the read request. The currentsignature 212 may be extracted from the memory 202 or it may begenerated on demand, upon receipt of the read request.

Alternatively, in some embodiments of an “active” tag, transmissions ofthe current signature 212 via the transceiver 204 are similarly effectedin response to detection of a read request via the transceiver 204. Inthis case, the availability of the power source 208 allows thecontroller 206 to transmit the current signature 212 at a longer rangethan for passive devices. Certain active tags also have the capabilityto switch into a passive mode of operation upon depletion of the powersource 208. In other embodiments of an active tag, transmissions of thecurrent signature 212 are effected via the transceiver 204 at instancesor intervals that are controlled by the controller 206. This can bereferred to as autonomous (or unsolicited) issuance of the currentsignature 212. To this end, the controller 206 needs to be continuouslypowered from the power source 208.

Active and passive tags may have other features that will be known tothose of skill in the art.

In still other cases, the power source 208 (either continually storing acharge or accumulating a sensed charge) can be connected to thecontroller 206 via a switch 210, which is optional. The switch 210 canbe toggled between a first state during which an electrical connectionis established between the power source 208 and the controller 206, anda second state during which this electrical connection is broken. Theswitch 210 is biased in the second state, and can be placed into thefirst state. Toggling into the first state can be achieved by a burst ofenergy that is sensed at a sensor (not shown) or by use of an activationelement. In various non-limiting embodiments, the activation element maybe a touch-sensitive pad on a surface of the tag 14, or a mechanicalcomponent (e.g., a button). Placing the switch 210 into the first statemay also trigger the controller 260 to change the current signature 212in the memory 202.

With reference now to FIG. 3, there is shown conceptually how thecurrent signature 212 stored in the memory 202 may change over time.Specifically, different versions of the current signature 212 (denotedS_(A) and S_(B)) are generated by an encoding function 302 implementedby the controller 206. For notational convenience, the current signature212 is used to denote which of the two signatures S_(A), S_(B) iscurrently stored in the memory 202. The encoding function 302 generatesthe signatures S_(A) and S_(B) by encoding a common “identifier”(denoted I_(D)) with a respective “additional data set” (denoted D_(A)and D_(B)) at respective time instants (denoted T_(A) and T_(B)). Thus,at T_(A), the signature S_(A) is generated by encoding the identifierI_(D) with the additional data set D_(A), whereas at T_(B), thesignature S_(B) is generated by encoding the identifier I_(D) with theadditional data set D_(B). While in this example, two time instants areshown and described, this is solely for simplicity, and it should beunderstood that in actuality, the current signature 212 may change manytimes.

The identifier I_(D) is constant, and in one embodiment conveysinformation about the item, animal, vehicle, piece of equipment, etc.,to which the tag 14 is affixed. Examples of such information include,without limitation: a serial number, a universal product code (UPC), avehicle registration number (VIN) and a customized identifier. Inanother embodiment, the identifier I_(D) conveys information about anexpected user of the vehicle, clothing or mobile communication device,computer, restricted access area, network, etc., to which the tag 14 isaffixed. Examples of such information include, without limitation: aname, an ID number, a driver's license number, an account number andlogin credentials.

In accordance with a non-limiting embodiment of the present invention,the additional data sets D_(A) and D_(B) are different, which makes bothsignatures S_(A), S_(B) different. In fact, the two signatures S_(A),S_(B) will appear scrambled relative to one another due to use of theencryption engine 222 within the encoding function 302. Morespecifically, the signatures S_(A) and S_(B) can be generated from theadditional data sets D_(A) and D_(B) in a variety of ways, two of whichwill be described herein below.

First Approach

In a first approach, described with reference to FIG. 4A, the identifierI_(D) is encrypted by the encryption engine 222 with a dynamickey—represented by the additional data sets D_(A), D_(B) themselves,resulting in the two signatures S_(A), S_(B). The two signatures S_(A),S_(B) will be different because the additional data sets D_(A), D_(B)are different. In fact, they will appear scrambled relative to oneanother when observed by someone who has not applied a decryptionprocess using a counterpart to the keys used by the encryption engine222.

It will be noted that in order to make the first approach practical, thereader 12 needs to have knowledge of which key (i.e., which of theadditional data sets D_(A), D_(B)) was used for encryption of a receivedone of the signatures S_(A), S_(B), in order to effect proper decryptionand recover the identifier I_(D). For this purpose, in order to assistthe reader 12 in identifying the correct key to be used for decryption,and with reference again to FIG. 2, the current signature 212 may beaccompanied by an index 214 also stored in the memory 202. The index 214may point the reader 12 to the correct key to be used. The reader 12 mayhave access to a key database (not shown) for this purpose.

For example, consider the case where the keys (in this case, theadditional data sets D_(A), D_(B)) correspond to outputs of thepseudo-random number generator 240 having a seed known a priori to thetag 14 and to the reader 12. Here, at T_(A), the index 214 may indicatethe sequential position in the output of the pseudo-random numbergenerator 240 that corresponds to the additional data set D_(A), whileat T_(B), the index 214 may indicate the sequential position in theoutput of the pseudo-random number generator 240 that corresponds to theadditional data set D_(B). The reader 12 can then easily find the valueoccupying the correct sequential position in the output of an identicallocal pseudo-random number generator and effect successful decryption ofthe received signature (S_(A) or S_(B)).

Alternatively, the keys (in this case, the additional data sets D_(A),D_(B)) are provided by the reader 12. This can be done where the reader12 (or an entity associated therewith) decides that a change in thecurrent signature 212 is required. As a variant, the reader 12 may issuea trigger which, when received by the controller 206, causes thecontroller 206 to effect a change in the current signature 212. In suchcases, changes to the key (and thus to the current signature 212) areeffected by the controller 206 in response to triggers received from thereader 12.

Second Approach

For other applications, the approach of FIG. 4B may be useful. Here, theidentifier I_(D) is augmented with differing scrambling codes (denotedC_(A) and C_(B)), and then encrypted by the encryption engine 222 with acommon key (denoted K), thus producing the two signatures S_(A), S_(B).The “additional data set” D_(A) used for encryption at T_(A) istherefore composed of the key K and the scrambling code C_(A), while the“additional data set” D_(B) used for encryption at T_(B) is composed ofthe same key K and the scrambling code C_(B). The encryption process canbe designed so that small differences (in terms of the number of bitswhere there is a difference) between the scrambling codes C_(A) andC_(B) will cause large differences (in terms of the number of bits wherethere is a difference) in the resultant signatures S_(A) and S_(B).Thus, the scrambling codes C_(A), C_(B) have the effect of scrambling(i.e., randomizing) the resultant signatures S_(A), S_(B).

The controller 206 is responsible for determining which scrambling codeis to be used to generate a particular signature at a particular timeinstant. The current version of the scrambling code can be stored in thememory 202 and is denoted 220 for convenience. It will be appreciatedbased on the above description that the scrambling code C_(A)corresponds to the current scrambling code 220 at T_(A) and that thescrambling code C_(B) corresponds to the current scrambling code 220 atT_(B).

Continuing with the second approach, several classes of embodiments arecontemplated for changing the current scrambling code 220. In a firstclass of embodiments relevant to the approach of FIG. 4B, the currentscrambling code 220 is changed in a way that can be predicted by thereader 12, that is to say, where the reader 12 (or an entity associatedtherewith) has knowledge of how each successive scrambling code isgenerated.

For example, the current scrambling code 220 can be changed each time(or, generally, each N^(th) time where N≧1) that the controller 206receives a read request or releases the current signature 212 inresponse to a read request. This can ensure that the current signature212 is different each N^(th) time that the controller 206 receives aread request. Alternatively, the current scrambling code 220 is changedevery the current scrambling code 220 can be changed every set period oftime (ex. every N seconds, minutes, hours, days, etc.). The variationsin the current scrambling code 220 may governed in a variety of waysthat are predictable to the reader 12. For example, the controller 206may implement a counter 230, whose output is incremented (by a step sizethat can equal unity or can be negative, for example) after each N^(th)time that the controller 206 responds to a read request received from anearby reader (or each N seconds, etc.). If the current scrambling code220 is set to correspond to the current output of the counter 230, thenthe scrambling codes C_(A), C_(B) used to generate the two signaturesS_(A), S_(B) will differ by the step size.

Alternatively, the controller 206 may implement the aforesaidpseudo-random number generator 240, which produces an output thatdepends on one or more previous values of the output and on a seed. Ifthe current scrambling code 220 is set to correspond to the currentoutput of the pseudo-random number generator 240, then the scramblingcodes C_(A), C_(B) used to generate the two signatures S_(A), S_(B) willdiffer in accordance with the characteristics of the pseudo-randomnumber generator 240.

Other variants will become apparent to those of skill in the art withoutdeparting from the scope of the present invention.

In a second class of embodiments relevant to the approach of FIG. 4B,the additional data sets D_(A), D_(B) are not only predicted by thereader 12 but are actually controlled by the reader 12. This can beuseful where the reader 12 (or an entity associated therewith) decidesthat a change in the current signature 212 is required. Alternatively,and recognizing that the key K is common to both of the additional datasets D_(A), D_(B), the reader 12 could supply the unique portions of theadditional data sets D_(A), D_(B), namely the scrambling codes C_(A),C_(B).

As a variant, the reader 12 may simply issue a trigger which, whenreceived by the controller 206, causes the controller 206 to effect achange in the current signature 212. In such cases, changes to thecurrent signature 212 are effected by the controller 206 in response totriggers received from the reader 12.

In a third class of embodiments relevant to the approach of FIG. 4B, itmay be desired to change the signatures S_(A), S_(B) in a stochasticway, that is to say, without the need to follow an underlying patternthat could be predicted by the reader 12.

For example, the controller 206 may implement the aforementionedgeo-location module 250, which is configured to output a current spatialposition of the tag 14 or of an item or person to which it is affixed.If the current scrambling code 220 is set to correspond to the currentoutput of the geo-location module 250, then the scrambling codes C_(A),C_(B) used to generate the two signatures S_(A), S_(B) will differ in astochastic fashion.

Alternatively, the controller 206 may implement a clock module 260,which is configured to determine a current time If the currentscrambling code 220 is set to correspond to a value measured by theclock module 260 (e.g., number of milliseconds elapsed since midnight ofthe day before), then the scrambling codes C_(A), C_(B) used to generatethe two signatures S_(A), S_(B) will differ in a stochastic fashion.

While the above embodiments have focused on temporal variations in thecurrent signature 212 stored in the memory 202 of the tag 14, it is alsowithin the scope of the present invention for the current signature 212stored in the memory 202 of two different tags to be different at acommon time instant (e.g., at a time when the tags are being read inbulk). This can be referred to as spatial scrambling. More particularly,with reference to FIG. 5, a plurality of tags 514 are affixed to anumber of units 506 of a particular article. The units 506 may bearranged on a pallet 508, on a shelf or in a container, for example. Totake a simple non-limiting example, the article in question can be apair of denim jeans of a certain brand, size, style and color. Ofcourse, the article could be any other item of which multiple units areavailable, such as a consumer product, food product, vehicle, etc. Otherpossibilities that may appear to one of skill in the art are within thescope of the present invention.

The tags 514 store respective signatures 510 that are each derived byencrypting an identifier 550 (common to the tags 514) and a respectiveone of a plurality of current scrambling codes 520 (different for thevarious tags 514) with a common key. The common identifier 550 can beused to identify the article in question (in this case, a pair of jeansof a particular brand, size, style, color, etc.). To ensure that thesignatures 510 appear scrambled while nevertheless encrypting the commonidentifier 550, approaches such as the following may be taken.

In one non-limiting approach, a centralized entity generates uniquecurrent scrambling codes 520 and unique signatures 510 for each of thetags 514. The tags 514 are pre-loaded with their respective uniquesignatures 510 before being affixed to the units 506. In this approach,the unique signatures 510 are fixed, as a result of which the tags 514can be greatly simplified since they do not need to perform anyprocessing functions. Practically speaking, this allows a distributor topurchase a plurality of tags 514 that have been pre-loaded with uniquesignatures 510 in order to securely identify the units 506 of aparticular article.

In another non-limiting approach, the tags 514 may each operate arespective clock module which, though structurally identical, may outputdifferent results, due to differences in oscillation characteristics(e.g., the oscillation crystals used, etc.) This will result indifferences between the current scrambling code produced based on anoutput of the clock module of one of the tags 514 and the currentscrambling code produced based on an output of the clock module ofanother one of the tags 514, albeit at the same time instant.

In yet another non-limiting approach, different current scrambling codes520 can be produced as a result of the tags 514 each operating arespective pseudo-random number generator using a different seed, whichcould be pre-loaded by the above mentioned centralized entity.

Still other ways of making the current scrambling codes 520 differentamong the various tags 514 are within the scope of the presentinvention.

It is noted that the signatures 510 will tend to be widely varying evenif the differences in the current scrambling codes 520 used to generatethem are small, this effect being due to application of an encryptionprocess, even when a common key is used. In fact, to an observer notequipped with the complementary key for decryption (which may be thesame as the common key in a symmetric encryption scenario), thesignatures 510 corresponding to the various units 506 on the pallet 508will appear scrambled. This provides protection against externalobservers (e.g., thieves, corporate intelligence investigators) who mayhave gathered knowledge of signatures output by one or more units of thearticle in the past (e.g., from a previous purchase—or knowledge of aprevious shipment—of the same brand, size, style and color of jeans) andare now on the lookout for the presence of units of the same article onthe pallet 508. On the other hand, by using the appropriate key in orderto decrypt any of the signatures 510, then no matter how diverse onesuch signature is from another, the common identifier 550 will berevealed alongside a stochastically derived scrambling code.

In order to allow the reader 12 to identify the appropriate key fordecryption, each of the signatures 510 may be accompanied by theaforesaid index 214 stored in the memory 202. The index 214 may pointthe reader 12 to the correct key for decryption. For example, the index214 could be a piece of public information such as a manufactureridentification code or a product category, such information being commonto the units 506 but sufficiently generic to be of little value to anoutside observer. This will allow the reader 12 (or an entity associatedtherewith) to select the correct key for decryption by accessing a tableof keys (not shown) on the basis of the index. Such an approach can beuseful to accelerate the decryption process and reduce the incidence offalse positives (successful but inadvertent decryption of the wrongidentifier) when multiple keys are potentially available to the reader12.

It should also be appreciated that the signatures 510 on the varioustags 514 can, in addition, be designed to change in a dynamic fashion(as described earlier), thus providing, in addition to spatialscrambling of the signatures 510, temporal scrambling of the signatures510 that leads to even greater security vis-à-vis external observation.

In view of the foregoing, it should thus be appreciated that a commonidentifier, which is encoded within a plurality of signatures that varyover space (for multiple tags) and/or time (for the same tag), can beextracted by the reader 12 (or an entity associated therewith) byutilizing the appropriate key for decryption. This allows the reader 12(or an entity associated therewith) to perform

-   -   (I) validation of the identifier based on the signature and/or        the scrambling code; and/or    -   (II) an action related to identification, based on the        identifier.

Both of these scenarios, which are not mutually exclusive, are nowdescribed in some detail.

In scenario (I), a dynamic scrambling code is used in the generation ofa signature that continually encodes the same identifier, and it is ofinterest to recover the current scrambling code to detect a potentialinstance of tag cloning. Accordingly, with reference to FIG. 6A, thereis shown a system that is similar to the system of FIG. 1. In addition,the system of FIG. 6A comprises a processing entity 610 that implementsa validation operation, as will be described herein below. In variousembodiments, the processing entity 610 referred to above may beconnected to the reader 12, or it may be a remote entity. Such a remoteentity may be reachable over a network, or it may be integrated with thereader 12. The system of FIG. 6A also includes a storage entity, such asa database 602, that is accessible to the processing entity 610 andstores a plurality of records 604, each associated with a respectiveidentifier. For the purposes of the present example, one can considerthat each identifier for which there exists a record in the database 602is indicative of a privilege to access certain property or make certaintransactions, although other scenarios are possible without departingfrom the scope of the present invention.

In accordance with one embodiment of the present invention, each of therecords 604 also comprises a field 606 indicative of zero or morescrambling codes 608 that were encoded in signatures which werepreviously received and which encoded the respective identifier for thatrecord. Thus, receipt of a particular signature that encodes theidentifier in a given one of the records 604 as well as one of thescrambling code(s) 608 stored in the corresponding field 606 willindicate that the particular signature has been previously received andtherefore its instant receipt may be indicative that a cloning attempthas been made.

More specifically, with reference to the flowchart in FIG. 7A, considerwhat happens following step 710 when a signature S_(X) is received at aparticular time instant by the reader 12. At the time of receipt,whether the signature S_(X) encodes any particular identifier orscrambling code is unknown to the reader 12. At step 730, an attempt todecrypt the signature S_(X) is made by the processing entity 610 using adecryption key K_(X). The decryption key K_(X) may be known in advanceto the processing entity 610. Alternatively, as shown in step 720, thesignature S_(X) may be accompanied by an index that allows theprocessing entity 610 to determine the appropriate decryption key K_(X).The result of the decryption attempt at step 730 is a candidateidentifier I_(X) and a candidate scrambling code, denoted C_(X).

At step 740, the processing entity 610 consults the database 602 basedon the candidate identifier I_(X) in an attempt to identify acorresponding record and extract therefrom a list of scrambling code(s)that have been received in the past in association with the candidateidentifier I_(X). For the purposes of the present example, it is usefulto assume that such a record exists (i.e., the “YES” branch is taken outof step 740), but if there is no such record, this may indicate thatthere is a high-level failure requiring further action. At step 750, theprocessing entity 610 compares the candidate scrambling code C_(X) tothe scrambling code(s) 608 in the field 606 of the record identified atstep 740 and corresponding to identifier I_(X).

If there is a match, this indicates that the scrambling code C_(X) hasbeen used in the past in association with the identifier I_(X). Undercertain conditions, this may lead the processing entity 610 to concludethat the validation operation was unsuccessful.

For example, if the signature S_(X) was expected to change at least asoften as every time that the tag on which it is stored was read, thenthe fact that the scrambling code C_(X) matches one of the scramblingcode(s) 608 stored in the field 606 of the record corresponding toidentifier I_(X) may lead the processing entity 610 to conclude that thevalidation operation was unsuccessful. Alternatively, if the signatureS_(X) was expected to change every N^(th) time that the tag on which itis stored was read, then the processing entity 610 may look at how manyof the scrambling code(s) 608 stored in the field 606 of the recordcorresponding to identifier I_(X) correspond to the scrambling codeC_(X), and if this number is greater than or equal to N, this may leadthe processing entity 610 to conclude that the validation operation wasunsuccessful. Alternatively still, if the signature S_(X) was expectedto change at least as often as every N seconds etc., then the processingentity 610 may look at how long ago it has been since a matching one ofthe scrambling code(s) 608 was first stored in the field 606 of therecord corresponding to identifier I_(X), and if this time interval isgreater than or equal to a pre-determined number of seconds, minutes,hours, days, etc., this may lead the processing entity 610 to concludethat the validation operation was unsuccessful.

Where a conclusion is reached that the validation operation wasunsuccessful, the privilege to access the property or make transactionsmay be revoked or at least questioned on the basis of suspected tagcloning.

On the other hand, if there is no match between the scrambling codeC_(X) and any of the scrambling code(s) 608 stored in the field 606 ofthe record corresponding to identifier I_(X), this may lead theprocessing entity 610 to conclude that the validation operation waspotentially successful. In such a case, the default privilege to accessthe property or make transactions may be granted (or at least notrevoked on the basis of suspected tag cloning).

In accordance with an alternative embodiment of the present invention,the field 606 in the record associated with each particular identifiermay be indicative of an “expected” scrambling code, i.e., the scramblingcode that should (under valid circumstances) be encoded in a signaturereceived from a tag that encodes the particular identifier.Alternatively, the field 606 in the record associated with eachparticular identifier may be indicative of an “expected” signature,i.e., the signature that should (under valid circumstances) be receivedfrom a tag that encodes the particular identifier. Thus, upon receipt ofthe signature S_(X), if it is found to correspond to the expectedsignature (or if the scrambling code C_(X) is found to correspond to theexpected scrambling code), this may lead the processing entity 610 toconclude that the validation operation was potentially successful. Onthe other hand, if there is no match between the signature S_(X) and theexpected signature stored in the database 602 (or between the scramblingcode C_(X) and the expected scrambling code), this may lead theprocessing entity 610 to conclude that the validation operation wasunsuccessful.

It should be appreciated that in the above alternative embodiments, theprocessing entity 610 may obtain knowledge of the expected scramblingcode or the expected signature by implementing plural pseudo-randomnumber generators for each of the identifiers, analogous to thepseudo-random number generator 240 implemented by the controller 206 ina given tag 14, which produces an output that depends on one or moreprevious values of the output and on a seed. Thus, the next output ofthe pseudo-random number generator implemented by the processing entity610 for a given identifier allows the processing entity 610 to predictthe scrambling code (or the signature) that should be received from atag legitimately encoding the given identifier. In another embodiment,the processing entity 610 may know what is the expected scramblingcode/signature because it has instructed the reader 12 to cause thisexpected scrambling code/signature to be stored in the memory of thetag.

In accordance with an alternative embodiment of the present invention,the database 602 simply comprises a running list of all signatures thathave been received in the past. Thus, upon receipt of the signatureS_(X), if it is found to correspond to one of the signatures on thelist, this may lead the processing entity 610 to conclude that thevalidation operation was unsuccessful. On the other hand, if there is nomatch between the signature S_(X) and any of the signatures stored inthe database 602, this may lead the processing entity 610 to concludethat the validation operation was potentially successful (or at leastnot unsuccessful).

It should also be appreciated that having obtained the identifier I_(X),the processing entity 610 may also perform an action related toidentification of an item associated with the particular tag thatencoded the identifier I_(X).

In a first example of an action related to identification, theprocessing entity 610 may simply note the fact that the item (bearingthe identifier I_(X)) was encountered in a vicinity of the reader 12.This information may be stored in a database (not shown) or sent as amessage, for example. In an inventory management scenario, theprocessing entity 610 may consult an inventory list and “check off” theitem as having been located, or may signal that the presence of aspurious item (that is not on the inventory list) has been detected.

In another example of an action related to identification, theprocessing entity 610 may consult another database (not shown) in orderto ascertain whether the identifier is on a list of identifiersassociated with individuals/objects permitted to access, or prohibitedfrom accessing, certain property. Examples of property include, withoutlimitation: computing equipment, a computer network, a building, aportion of a building, an entrance, an exit and a vehicle.

In another example of an action related to identification, theprocessing entity 610 may consult another database (not shown) in orderto ascertain whether the identifier is on a list of identifiersassociated with individuals permitted to effect, or prohibited fromeffecting, a transaction, which could be a financial transaction or alogin to controlled online content, for example.

FIG. 7B shows a variant where multiple keys are possible but no index(or one that does not permit identification of the appropriatedecryption key) is provided along with the signature S_(X).Specifically, taking the “NO” branch after step 750 does not concludethe validation operation. Rather, the validation operation goes throughstep 770 where a next key is selected and then the validation operationreturns to step 730, whereby steps 730 through 770 are re-executed untilthe earlier occurrence of (i) taking the “YES” branch at step 750 and(ii) exhaustion of all keys, which can result in the equivalent oftaking the “NO” branch out of 740 (i.e., this may indicate that there isa high-level failure requiring further action).

It should be appreciated that in the above embodiments, encryption anddecryption can be effected using various techniques known in the art,including encryption using a symmetric key, an asymmetric key pair, apublic/private key pair, etc., as well as in accordance with a varietyof algorithms and protocols For example, RSA and ECC are suitableexamples of asymmetric encryption algorithms, while AES, DES, andBlowfish are suitable examples of symmetric algorithms. Still otherpossibilities exist and are within the scope of the present invention.

In the above example with reference to FIGS. 6A, 7A and 7B, although asingle reader was described and illustrated, it should be appreciatedthat it is within the scope of the present invention to provide amulti-reader architecture, as shown in FIG. 6B. A plurality of readers1012 are connected to each other and to a centralized control entity1010 by a network 1030, which can be a public packet-switched network, aVLAN, a set of point-to-point links, etc. In such a case, thecentralized control entity 1010 (e.g., a network controller) canimplement the functionality of the processing entities 610, includingencryption and validation. To this end, the centralized control entity1010 maintains a master database 1020, which includes the equivalent ofa consolidated version of various instances of the database 602previously described as being associated with the reader 12 in thesingle-reader scenario.

Thus, decryption and validation can be performed entirely in thecentralized control entity 1010. Alternatively, certain functionality(such as decryption) can be performed by the readers 1012 while otherfunctionality (such as validation) can be performed by the centralizedcontrol entity 1010. Still alternatively, the processing entities 610can inter-operate amongst themselves in the absence of the centralizedentity 1010, thereby to implement decryption on a local basis, and thevalidation operation in a joint fashion. In such a distributed scenario,the master database 1020 can still be used, or the processing entities610 can communicate with one another to share information in theirrespective databases 602.

In scenario (II), a dynamic key is used in the generation of a signaturethat encodes a constant identifier, and it is of interest to recover theunderlying identifier despite the time-varying key. Accordingly, withreference now to FIG. 8, there is shown a system that is similar to thesystem of FIG. 1. In addition, the system of FIG. 8 comprises aprocessing entity 810 that implements an identification operation, aswill be described herein below. The processing entity 810 may beconnected to the reader 12, or it may be a remote entity. Such a remoteentity may be reachable over a network, or it may be integrated with thereader 12. It should be understood that the system in FIG. 8 is beingshown separately from the system in FIG. 6; however, it is within thescope of the present invention to combine the functionality of bothsystems.

With reference to the flowchart in FIG. 9, consider what happensfollowing step 910 when a signature S_(Y) is received from a particulartag at a particular time instant by the reader 12. The signature S_(Y)is assumed to have been generated by encrypting an identifier I_(Y)using an encryption key that varies in a dynamic fashion. To this end,the particular tag may have generated the dynamic encryption key basedon, for example:

-   -   the output of the aforementioned clock module 260 (e.g., in        terms of seconds, minutes or hours of elapsed time since an        event known also to the processing entity 810);    -   the output of the aforementioned geo-location module 250;    -   an index;    -   a seed for use by a pseudo-random number generator.

Still other possibilities are within the scope of the present invention.The decryption key can then be determined based on the above quantity.For example, the decryption key could be the above-mentioned output ofthe clock module or the geo-location module. Alternatively, theencryption key could be the output of a table or a pseudo-random numbergenerator (both known to the processing entity 810) based on theabove-mentioned seed, or at a position that corresponds to theabove-mentioned index. In the latter case, the index or seed can besupplied along with the signature S_(Y).

In accordance with the present embodiment, once the signature S_(Y) isread by the reader 12, the processing entity 810 is expected todetermine the appropriate decryption key, denoted K_(Y). Accordingly, atstep 930, the processing entity 810 first determines a dynamic parameterthat will allow the decryption key K_(Y) to be determined. Examples ofthe dynamic parameter include:

-   -   the output of a clock module (which attempts to emulate the        aforementioned clock module 260) at the time of receipt of the        signature S_(Y) (e.g., in terms of seconds, minutes or hours of        elapsed time since a known event);    -   the output of a geo-location module (which can be similar to the        aforementioned geo-location module 250);    -   the index or seed provided along with the signature S_(Y).

Next, at step 940, the processing entity 810 obtains the decryption keyK_(Y) based on the dynamic parameter determined at step 930. Forexample, where the dynamic parameter corresponds to the output of aclock module or a geo-location module, the decryption key K_(Y) could bethe dynamic parameter itself. Alternatively, where the dynamic parameteris an index or a seed, the decryption key K_(Y) could be the output ofthe aforementioned table or pseudo-random number generator known to theprocessing entity 810, at a position that corresponds to the receivedindex, or using the received seed.

Once the decryption key has been obtained, the signature S_(Y) isdecrypted at step 950 using the decryption key. This leads to extractionof the identifier I_(Y). It is noted that a scrambling code was notrequired in this embodiment, although its use is not disallowed.

Having obtained the identifier I_(Y), the processing entity 810 proceedsto step 960, where it performs an action related to identification of anitem associated with the particular tag that encoded the identifierI_(Y).

In a first example of an action related to identification, theprocessing entity 810 may simply note the fact that the item (bearingthe identifier I_(Y)) was encountered in a vicinity of the reader 12.This information may be stored in a database (not shown) or sent as amessage, for example. In an inventory management scenario, theprocessing entity 810 may consult an inventory list and “check off” theitem as having been located, or may signal that the presence of aspurious item (that is not on the inventory list) has been detected.

In another example of an action related to identification, theprocessing entity 810 may consult another database (not shown) in orderto ascertain whether the identifier is on a list of identifiersassociated with individuals/objects permitted to access, or prohibitedfrom accessing, certain property. Examples of property include, withoutlimitation: computing equipment, a computer network, a building, abuilding, a portion of a building, an entrance, an exit and a vehicle.

In yet another example of an action related to identification, theprocessing entity 810 may consult another database (not shown) in orderto ascertain whether the identifier is on a list of identifiersassociated with individuals permitted to effect, or prohibited fromeffecting, a transaction, which could be a financial transaction or alogin to controlled online content, for example.

It should be appreciated that the processing entity 810 may also performan action related to validation of the identifier I_(Y) in conjunctionwith the above action related to identification. Specifically, inaccordance with one embodiment of the present invention, the processingentity may consult a variant of the aforementioned database 602, whereeach of the records 604 now includes a field indicative of zero or moresignatures which were previously received and which encoded therespective identifier for that record. Thus, receipt of a particularsignature that encodes the identifier in a given one of the records 604as well as one of the signature(s) stored in the corresponding fieldwill indicate that the particular signature has been previously receivedand therefore its instant receipt may be indicative that a cloningattempt has been made.

In the above example with reference to FIGS. 8 and 9, although a singlereader was described and illustrated, it should be appreciated that itis within the scope of the present invention to provide a multi-readerarchitecture, as in FIG. 6B.

Also, those skilled in the art will appreciate that in some embodiments,the functionality of any or all of the processing entity 610, theprocessing entity 810, the reader 12 and the readers 1012 may beimplemented using pre-programmed hardware or firmware elements (e.g.,application specific integrated circuits (ASICs), electrically erasableprogrammable read-only memories (EEPROMs), etc.), or other relatedcomponents. In other embodiments, the functionality of the entity inquestion may be achieved using a computing apparatus that has access toa code memory (not shown) which stores computer-readable program codefor operation of the computing apparatus, in which case thecomputer-readable program code could be stored on a medium which isfixed, tangible and readable directly by the entity in question (e.g.,removable diskette, CD-ROM, ROM, fixed disk, USB drive), or thecomputer-readable program code could be stored remotely buttransmittable to the entity in question via a modem or other interfacedevice (e.g., a communications adapter) connected to a network(including, without limitation, the Internet) over a transmissionmedium, which may be either a non-wireless medium (e.g., optical oranalog communications lines) or a wireless medium (e.g., microwave,infrared or other transmission schemes) or a combination thereof.

While specific embodiments of the present invention have been describedand illustrated, it will be apparent to those skilled in the art thatnumerous modifications and variations can be made without departing fromthe scope of the invention as defined in the appended claims.

1. A method, comprising: generating a first signature by encoding anidentifier with a first additional data set at a first time instant;responding to a first read request from a tag reader by releasing thefirst signature; generating a second signature by encoding theidentifier with a second additional data set at a second time instant,the second additional data set being different from the first additionaldata set; and responding to a second read request by releasing thesecond signature. 2.-67. (canceled)